* viz: add render golden tests
This branch adds golden tests for the viz install. This would be
useful to track changes in render as more changes are added.
This also moves the common code that is used across extensions
to generate diffs into `testutil` to be able to be used widely.
Signed-off-by: Tarun Pothulapati <tarunpothulapati@outlook.com>
Tarun Pothulapati